Rempfer, C. | Search bioRxiv

bioRxiv2021

Autopolyploidization affects transcript patterns and gene targeting frequencies in Physcomitrella

Qualitative changes in gene expression after an autopolyploidization event, a pure duplication of the whole genome, might be relevant for a different regulation of molecular mechanisms between angiosperms growing in a life cycle with a dominant diploid sporophytic stage and the haploid-dominant bryophytes. Whereas angiosperms repair DNA double strand breaks (DSB) preferentially via non-homologous end joining (NHEJ), in bryophytes homologous recombination (HR) is the main DNA-DSB repair pathway facilitating the precise integration of foreign DNA into the genome via gene targeting (GT). Here, we studied the influence of ploidy on gene expression patterns and GT efficiency in the moss Physcomitrella using haploid plants and autodiploid plants, generated via an artificial duplication of the whole genome. Single cells (protoplasts) were transfected with a GT construct and material from different time-points after transfection was analysed by microarrays and SuperSAGE sequencing. In the SuperSAGE data, we detected 3.7% of the Physcomitrella genes as differentially expressed in response to the whole genome duplication event. Among the differentially expressed genes involved in DNA-DSB repair was an upregulated gene encoding the X-ray repair cross-complementing protein 4 (XRCC4), a key player in NHEJ. Analysing the GT efficiency, we observed that autodiploid plants were significantly GT suppressed (p<0.001) attaining only one third of the expected GT rates. Hence, an alteration of global transcript patterns, including genes related to DNA repair, in autodiploid Physcomitrella plants correlated with a drastic suppression of HR.

plant biology↗

bioRxiv2020

Stable Protein Sialylation in Physcomitrella

Recombinantly produced proteins are indispensable tools for medical applications. Since the majority of them are glycoproteins, their N-glycosylation profiles are major determinants for their activity, structural properties and safety. For therapeutical applications, a glycosylation pattern adapted to product and treatment requirements is advantageous. Physcomitrella (Physcomitrium patens, moss) is able to perform highly homogeneous complex-type N-glycosylation. Additionally, it has been glyco-engineered to eliminate plant-specific sugar residues by knock-out of the {beta}1,2-xylosyltransferase and 1,3-fucosyltransferase genes ({Delta}xt/ft). Furthermore, P. patens meets wide-ranging biopharmaceutical requirements such as GMP compliance, product safety, scalability and outstanding possibilities for precise genome engineering. However, all plants, in contrast to mammals, lack the capability to perform N-glycan sialylation. Since sialic acids are a common terminal modification on human N-glycans, the property to perform N-glycan sialylation is highly desired within the plant-based biopharmaceutical sector. In this study, we present the successful achievement of protein N-glycan sialylation in stably transformed P. patens. The sialylation ability was achieved in a {Delta}xt/ft moss line by stable expression of six mammalian coding sequences combined with targeted organelle-specific localization of the encoded enzymes responsible for synthesis, activation, transport and transfer of sialic acid. Production of free and (CMP)-activated sialic acid was proven. The glycosidic anchor for the attachment of terminal sialic acid was generated by the introduction of a chimeric human {beta}1,4-galactosyltransferase gene under the simultaneous knock-out of the gene encoding the endogenous {beta}1,3-galactosyltransferase. Functional complex-type N-glycan sialylation was confirmed via mass spectrometric analysis of a stably co-expressed recombinant human protein.

bioengineering↗